1. Field of the Invention
The present invention relates to an image restoration apparatus, an image restoration method, a program and a recording medium for restoring the degradation of an image obtained as image data by a digital camera or the like.
2. Description of the Related Art
Conventionally, various techniques have been proposed to restore the degradation of an image obtained as image data by use of a light receiving element array such as CCD. Image degradation is that the actually obtained image is degraded compared to the ideal image to be obtained from the object to be taken. For example, an image obtained by use of a digital camera is degraded by aberrations depending on, e.g. the aperture value, the focal length and the position of focus point, and is further degraded by an optical low pass filter for preventing spurious resolution. The image is also degraded by a camera-shake caused at the time of photo-taking.
On such a degraded image, restoration to approximate the obtained image to the ideal image by modeling image degradation has conventionally been performed. For example, image restoration has been performed by, regarding image degradation as being caused while an optical flux to be incident on each light receiving element is spreading according to the Gaussian distribution, causing a restoration function to act on the entire image or causing a filter that enhances an edge of the image to act on the entire image.
However, image degradation is not always caused on the entire image. For example, when an object of a geometric pattern or with a monochromatic background is photographed or when an original for character recognition is scanned, an area not affected by degradation is present in the image.
When image restoration is performed on the entire image, there are cases where an area not requiring restoration is also adversely affected. For example, when restoration is performed on an area where noise and an edge are present, ringing and noise enhancement are caused, so that the area not requiring restoration is also adversely affected.
To solve this problem, a technique has already been proposed to perform image restoration while influence of ringing and the like is avoided by performing image processing only on a specific area.
However, according to this technique, since the area is divided into two kinds of areas, namely, an area to be restored and an area not to be restored, discontinuity on the border between the two kinds of areas is conspicuous, so that the restored image is unnatural.